Salmon and many other varieties of fish are now commonly raised in offshore pens. At times the fish may need to be transferred from one area to another for a variety of reasons. For instance, should a net pen need servicing the fish may need to be transferred. When the fish are to be harvested they will need to be transferred. If the fish are affected with sea lice it might be beneficial to transfer them through a cleaning process. An objective of any fish transfer is to perform the transfer will little or no damage to the fish. This includes minimizing the stress on the fish.
The most common way of transferring fish is by pump. Fish are transferred or “pumped” live for grading, transporting, inoculation, or any other reason by the use of specialty pumps. These pumps are typically located on boats, barges and docks, and large hoses are used to enter into the cage housing the fish. The hoses are usually constructed with a metal cone at the suction end. Nets are used to crowd the fish to the cone where they are sucked into the hose.
Fish are preferably transferred using specialty pumps that are capable of moving fluid without an inline impeller. Known pumps include: SILKSTREAM™, TRANSVAC®, and Magic Valley, to name a few. SILKSTREAM™ is a Coanda effect pump as disclosed in U.S. Pat. No. 7,462,016 providing a technology for pumping larger fish in a manner that reduces injury and stress, compared to previous technology, to meet the demands for larger high quality fish.
Conventionally a net is used within the fish pen to crowd the fish wherein the fish are randomly sucked into a fish transfer pump. When fish are drawn through a proper fish pump they are not subjected to any moving parts of the pump. Fish traveling through the fish pump head first pass from a low pressure intake to a high velocity pump area, sea lice which are attached by being hooked to scales are effectively removed by the faster current.
In particular, the SILKSTREAM™ pump enters water to a tube concentrically at a high velocity on a curved cone surface to create inlet suction. For example, a 10 inch pump commonly used on salmon fish requires approximately 2,000 GPM for a 2 meter lift. The inlet water with fish will be approximately 1,500 GPM. The water stream tube surface will triple velocity in less than 4 inches. The SILKSTREAM™ pump has found to be exceptionally beneficial in the removal of sea lice when the fish is drawn through the pump head first.
Sea lice develop through several life stages. During adult and sub adult stages, the sea lice can be mobile and attach to salmon by hooking on scales or with a filament. The velocity difference between the water and the fish remove sea lice. Fish that enter a current head first receive higher velocity water from tail to head, which easily detaches hooked on sea lice and the filament. Fish that enter a current tail first receive a velocity gradient from tail to head and the hooked on lice often stay hooked. Test results for Salmon entering water streams of 0.3 to 1 psi from head to tail produces almost no sea lice removal until over 1 psi while tail to head 0.3 psi is effective to detach lice tested.
It is recognized that captive salmon prefer swimming into water currents when possible because they have very limited ability to travel backward. This is especially true when the fish are being crowded during harvest pumping. The suction of the pump traditionally creates a current that encourages salmon to swim away from the pump suction cone inlet as they draw closer, increasing the probability that the fish is drawn into the pump tail first. In most applications, it is preferred to have fish moved head first.
Thus, what is lacking is an apparatus that can be used with fish pumps at harvest, or for sea lice removal, to assure the fish is facing head first during the fish transfer to minimize or eliminate harming the fish, and maximize sea lice removal with less crowding and stress.